Liquid crystal display devices have been used in various small-sized display devices because they are operated at a low voltage, low consumption of electric power and being enable thin display. Meanwhile, with the recent utilization of liquid crystal display devices in wider applications such as apparatuses for office automation, televisions and the like, there has rapidly arisen a requirement for high-performance large-sized liquid crystal display device having such display capacity and display quality as to surpass those of conventional CRT display devices. However, even in the case of active matrix-driven liquid crystal display devices now employed in liquid crystal televisions, their modification into a large-sized device of low cost is not easy owing to the complex production process and low yield, as long as a currently used nematic liquid crystal is employed therein. Also, in the case of simple matrix-driven STN type liquid crystal display devices, the driving in large capacity is not easy; the response time has a limitation; and the video rate display is difficult. Thus, nematic liquid crystal display devices are unable to satisfy the above requirement for high-performance liquid crystal display device.
Under such a situation, attention is being paid to a liquid crystal display device using a ferroelectric liquid crystal substance, which is a quick response liquid crystal display device. The surface-stabilized ferroelectric liquid crystal (SSFLC) device reported by N. A. Clark and S. T. Lagerwall is drawing attention because of the quick response (which has been unobtainable with conventional liquid crystal display devices) and wide viewing angle, and the switching property has been studied in detail. A number of SSFLC substances are in actual production for use in SSFLC devices of desired properties. However, these SSFLC substances have various problems. For example, they have an insufficient threshold; they have poor contrast because, for example, their layer structure is a chevron structure; they show no quick response; their alignment is difficult to control and their bistability (this is one of the biggest characteristics of SSLFC) is difficult to achieve; and their alignment is destructed by mechanical impact and its recovery is difficult.
Devices employing switching mechanisms different from that of SSFLC are also being developed simultaneously. The switching between three stable states, of a liquid crystal substance having an antiferroelectric phase (said substance is hereinafter referred to as antiferroelectric liquid crystal substance) is one of such new switching mechanisms (Japanese Journal of Applied Physics, Vol. 27, p. L729, 1988).
Antiferroelectric liquid crystal substances each have three stable states, i.e. the same two uniform states (Ur, Ue) as seen in ferroelectric liquid crystal substances and a third state. That this third state is an antiferroelectric phase, we reported by Japanese Journal of Applied Physics, Vol. 28, p. L1265, 1989). Such switching between three stable states is the first characteristics of antiferroelectric liquid crystal substances. The second characteristic of antiferroelectric liquid crystal substances is that each of them has a clear threshold for an applied voltage. The third characteristic of ferroelectric liquid crystal substances is that they have good memory effect. By using an antiferroelectric liquid crystal substance having these excellent characteristics, there can be achieved a liquid crystal display device giving quick response and good contrast.
As another important characteristic of antiferroelectric liquid crystal substances, there can be mentioned a fact that their layer structure can be easily switched by an electric field (Japanese Journal of Applied Physics, Vol. 28, p. L119, 1989, Japanese Journal of Applied Physics, Vol. 29, p. L111, 1990). Owing to this fact, it becomes possible to produce a liquid crystal display device having little defects and having self-recoverability of alignment and consequently produce a liquid crystal display device capable of giving excellent contrast. As the antiferroelectric liquid crystal display devices, there are known those described in Japanese Patent Application Kokai (Laid-Open) Nos. 213390/1989, 316339/1989, 316367/1989, 316372/1989 and 28128/1990 and Liquid Crystals, Vol. 6, p. 167, 1989. Owing to the short history of studies on antiferroelectric liquid crystal substances, the number of hitherto known antiferroelectric liquid crystal substances is not large as compared with the number of ferroelectric liquid crystal substances, but the number of on the increase with the progress of said studies.
When the antiferroelectric liquid crystal substances produced heretofore are looked from the response time, many of them are not sufficient in response time and the number of said substances applicable to in the same manner as in Example 1 (8). As a result, the display devices capable of giving a fine and precise image is not so large. The antiferroelectric liquid crystal substances have been slightly disadvantageous in this point, as compared with conventional ferroelectric liquid crystal substances. Therefore, if there can be developed an antiferroelectric liquid crystal substance giving very quick response at room temperature or thereabouts, it is very advantageous for the realization of a display device capable of giving a fine and precise image. The present invention has been made under such a circumstance and provides an antiferroelectric liquid crystal substance giving very quick response at room temperature or thereabouts.